1. Field of the Invention
The present invention relates to an electronic still camera and, more particularly, to an electronic still camera for recording digital still-image signals generated by an image pickup device such as a charged coupled device (CCD), in a recording medium such as a so-called "memory card" containing a semiconductor memory or the like.
2. Description of the Related Art
Thanks to recent advances made in semiconductor devices and digital-signal processing technology, various types of electronic still cameras have been developed which record still-image signals generated by a solid-state image-pickup device such as a CCD, in a socalled memory card which contains a semiconductor memory. The still-image signals recorded in the memory card are supplied to an image-reproducing apparatus such as a TV receiver, which reproduces an image from these signals.
The memory card has but a limited storage capacity, and the still-image signals generated by the image-pickup device are subjected to a signal-processing, such as luminance/chrominance (Y-C) separation, and then to data compression, before they are recorded in the memory card.
FIG. 8 is a schematic block diagram illustrating a conventional electronic still camera of the type described above. As is shown in FIG. 8, the camera comprises an optical lens system 1 having an aperture diaphragm, a CCD 2, an amplifier 3, a video processor 4, two A/D converters 5 and 6, a buffer memory 7, a data compressing unit 8, and a memory card 9. The light reflected from an object passes through the lens system 1 and is applied to the CCD 2. The CCD 2 converts the light into still-image signals. These signals are amplified by the amplifier 3 and input to the video processor 4. The video processor 4 performs Y-C separation on the input signals. More precisely, the processor 4 separates each signal into a luminance signal and a chrominance signal. The luminance signals are supplied to the A/D converter 5 and converted into digital luminance signals, whereas- the chrominance signals are supplied to the A/D converter 6 and converted into digital chrominance signals. The digital signals output by these A/D converters 5 and 6 are stored into the buffer memory 7. Y-C signals, each composed of a luminance signal and a chrominance signal, are read from the buffer memory 7, and are input to the data-compressing unit 8. The unit 8 compresses the Y-C signals, and the compressed Y-C signals are recorded in the memory card 9.
The video processor 4 requires a long time to separate the signals output from the CCD 2 into a luminance signal and a chrominance signal. The A/D converters 5 and 6 also require much time to convert the luminance and chrominance signals into digital signals, and the data-compressing unit 8 also requires much more time to compress the Y-C signals. Consequently, a considerably long period of time passes from the time the CCD converts the light into still-image signals to the time Y-C signals are recorded in the memory card 9. This period is particularly long when the data compressing unit 8 is of the type which performs a high level data compression such as adaptive discrete cosine transform (ADCT), thereby to generate high-quality image signals. The buffer memory 7 needs to keep storing the still-image signals (more precisely, the luminance signals and the chrominance signals) for a greater part of this long period. Hence, the buffer memory 7 must have a great storage capacity in order to enable the user of the electronic still camera to take many pictures of an object at short intervals.
To shorten the time required to process the still-image signals output by the CCD 2 into Y-C signals which can be recorded in the memory card 9, the camera needs to have a very complex hardware configuration, and must inevitably be very large and expensive.